R.-f. circuit selector or the like



Dec. 3, 1957 R. A. DAVIS 2,815,443

R-F gmcurr SELECTOR OR THE LIKE Filed June '23, 1955- R038 A DAVISINVENTOR. K

HIS ATTORNEY United States Patent R.-F. CIRCUIT SELECTOR OR THE LIKERoss A. Davis, Los Angeles, Calif.

Application June 23, 1955, Serial No. 517,460

7 Claims. (Cl. 250-20) This invention relates to R.-F. couplers and,more particularly, to an electronic circuit which provides for thesequential coupling of signals between a plurality of R. F. circuits,for example the sequential coupling of two separate antennas to theinput stages of associated radio apparatus.

In a co-pending application, Serial No. 503,190, filed April 22, 1955 bythis inventor, there is described a multiple receiving or transmittingantenna system particularly suited for automobiles in which a pluralityof spacephased signals is derived from one or more openings in thestructure, and are utilized sequentially by the associated receivingapparatus. A number of devices have been proposed for effecting thesequential coupling between the antennas and the input circuits of thereceiver, one of them being the mechanical system described in anapplication entitled Sequential Coupler for R.-F. Circuits, and in thename of the same inventor as this application. An electronic system foreifecting such sequential coupling is desirable because of its freedomfrom moving parts. While some gating systems are shown in the prior artin connection with diversity antennas, they are generally subject toundesirable coupling of the control signal into the input circuits ofthe receiver. Such extraneous signals result in undesirable noise in andspurious responses of the receiver.

Therefore, it is an object of this invention to provide an electronicR.-F. circuit selector which permits sequential operation of thecircuits, for example antenna circuits, and which is free fromintroduction of undesired signals into the receiver.

According to the present invention a source of signals varyingalternately between two conditions is utilized to alternately bring toconduction two sets of normally nonconducting diodes, or conversely, toalternately cut off two sets of normally conducting diodes, each setbeing effectively in shunt with an associated inductance which is, inturn, coupled to the tuning inductance for each of the associated R.-F.circuits, for example antenna circuits. The inductances to which thediodes are coupled are center tapped, the center taps being grounded.During periods of non-conduction of each diode set, any stray signalspassing through the diodes as a result of interelectrode capacity arecancelled out in the center-tapped inductance or in the anode circuit ofthe sequential mixer. During the period when the diode sets areconducting, any leakage of control signals into the associatedinductance is of no significance since that inductance presentssubstantially a short circuit to the associated tuning inductance.Therefore, the tuning inductances associated with the separate R.-F.circuits, or antennas, are alternately damped to a high degree.Correspondingly, in those damped periods, little signal arrives at thesequential mixer stage from the associated circuit. The sequentiallyarriving signals appear at the anode of the sequential mixer. Thecircuit may be easily adapted to transmitter applications.

2,815,443 Patented Dec. 3, 1957 ICC The features of the presentinvention which are believed to be novel are set forth withparticularity in the appended claims. The present invention, both as toits organization and manner of operation, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description, taken in connection with the accompanyingdrawing, in which:

The sole figure is a schematic diagram of one embodiment of the presentinvention.

In the sole figure, antenna 10 is represented as a closed loop and maybe the boundary surrounding a discontinuity in a structure or vehiclebody. Of course, any other type of antenna may suflice. Signals areconducted from antenna 10 through conductor 11 to antenna tuninginductance 12 which is coupled through condenser 13 to grid 14 of vacuumtube 15. correspondingly, signals from antenna 16 are coupled throughconductor 17 to antenna tuning inductance 18 which, in turn, is coupledthrough condenser 19 to grid 20 of vacuum tube 15. Damping inductance 21is inductively coupled to tuning inductance 12 and is center tapped,with its center tap grounded. One end 22 of inductance 21 is connectedto anode 23 of duo-diode 24. The remaining end 25 of inductance 21 isconnected to anode 26 of duo-diode 24. Cathodes 27 and 28 areinterconnected. In fact, of course, a tube having a single cathode and apair of diode plates may be utilized in this operation. Correspondingly,two separate diodes may be utilized. Triodes may be utilized but aregenerally unnecessary for this type of application. Damping inductance29 is inductively coupled to tuning inductance 18 and has a center tapwhich is grounded. One terminal 30 of inductance 29 is connected toanode 31 of duo-diode 32, the remaining end 33 of inductance 22 beingconnected to anode 34 of that duo-diode. Cathodes 35 and 36 of duo-diode32 are interconnected. Oscillator 37 which, for this application, shouldoperate outside the range of audible frequencies, has an output tankcircuit including inductance 38 and condenser 39. One end 40 ofinductance 33 is connected to the interconnected cathodes 27 and 28. Theremaining end 41 of inductance 33 is connected to interconnectedcathodes 35 and 36. Oscillator 37 need not be a sine wave oscillator butmust be capable of producing alternately and periodically twoconditions. For example, oscillator 37 may be a square wave generator ofany circuit configuration. By reason of the connection of the two setsof cathodes to opposite ends of inductance 38, the control signalssupplied to the two sets of cathodes are out of phase with each other.The amplitude of the control signal from oscillator 37 must besufficiently great so that it will produce conduction sufiicient to dampthe strongest signals received.

The circuit of the sole figure operates as follows. Assume for themoment that oscillator 37 is a sine Wave oscillator. During one half ofthe cycle, duo-diode 24 will operate and during the other half of thecycle duodiode 32 will operate. When duo-diode 24 is operating orconducting, there is substantially a short circuit across dampinginductance 21 which reflects as a very low impedance across tuninginductance 12 and clamps it to the point where substantially no signalpasses from antenna 10 to grid 14. During the next half cycle duodiode24 is non-conductive and duo-diode 32 conducts with a resultant shortcircuiting of damping inductance 29. This reflects as a very lowimpedance across tuning inductance 18 and substantially eliminates anyapplication of signals from antenna 16 to grid 20. As the oscillatorcontinues, the alternate operation of duo-diodes 24 and 32 occurs.During the time when duo-diode 24 is not conducting there exists a smallamount of capacity between anode 26 and cathode 27 and between anode 23and cathode 28. However, any control signals from oscillator 37 whichpass through this inter-electrode capacitance of duo-diode 24 opposeeach other in damping inductance 21 by reason of its balanced and centertapped nature. Therefore, the resultant flux is zero and none of thecontrol signal leaks back into tuning inductance 12. Further,cancellation of stray signals occurs at the interconnected anodes ofsequential mixer 15. The same analysis applies to the non-conductingcondition of duo-diode 32. Thus, sequential coupling of signals fromantennas and 16 to grids 14 and 20, respectively, and hence to the inputstages of the receiver which follow is efiected while at the same timepreventing leakage of control oscillator signals to the receiver. Bybreaking grounding lead 42 at point X and connecting in series a biasingbattery poled with its positive terminal grounded and having a voltagejust sufiicient to bias duo-diodes 24 and 32 to conduction in theabsence of signals from oscillator 37 the operation of the circuit ofthe sole figure varies slightly but the results are substantially thesame. With this circuit biased as indicated, both tuning coils 12 and 18are normally damped heavily and a positive impulse from oscillator 37 ofsuflicient magnitude to overcome the bias voltage is required to effectcoupling from antennas 10 and 16 to their respective grids in amplifiertube 15.

It should be noted that if more than two R.-F. circuits are to beselected sequentially the present concepts may be utilized by simplyincreasing the number of phases generated by oscillator 37, adding thedesired number of damping circuits each controlled by the oscillator,and providing the appropriate number of mixing grids and associatedcircuits.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects, and, therefore, the aim in theappended claims is to cover all such changes and modifications as fallwithin the true spirit and scope of this invention.

I claim:

1. An antenna selector including first and second antenna inputterminals adapted for connection to first and second antennas,respectively, a sequential mixer circuit having first and second inputcircuits and an output circuit, a first tuning inductance coupledbetween said first antenna input circuit and said first input circuit ofsaid mixer circuit, a second tuning inductance coupled between saidsecond antenna input terminal and said second input terminal of saidmixer circuit, a source of control signals alternating between first andsecond conditions, first means inductively coupled to said first tuninginductance and responsive to signals from said control source forinductive damping of said first tuning inductance during said firstcondition of said control signal and second means inductively coupled tosaid second tuning inductance and responsive to signals from saidcontrol source for inductive damping of said second tuning inductanceduring said second condition of said control signal, said alternatinginductive damping of said first and second tuning inductances being of amagnitude sufficient to alternately substantially prevent the couplingof a signal from the respective said antennas to said mixer circuitduring said damping.

2. Apparatus according to claim 1 in which said source of controlsignals is a sine Wave oscillator operating at frequencies above theaudio range.

3. Apparatus according to claim 1' in which said first and second meanseach includes a center tapped inductance with such center tap connectedto ground potential, anda pair of diodes having their respective anodescouplcd to opposite ends of the associated inductance, and havingeffectively a single cathode coupled to said control signal source.

4. Apparatus according to claim 3 in which the said diodes are vacuumdiodes.

5. Apparatus according to claim 3 in which said signal source has firstand second output terminals providing at any one instant said controlsignal in opposite conditions, said diode cathodes associated with saidfirst means being coupled to said first output terminals, and said diodecathodes associated with said second means being coupled to said secondoutput terminals.

6. Apparatus according to claim 5 in which said first conditioncorresponds to conduction of said diodes and said second conditioncorresponds to non-conduction of said diodes.

7. A circuit for the selective translation of signals from a pluralityof R.-F. circuits, each including an inductance, said selective circuitincluding a source of control signals alternating between first andsecond conditions, means inductively coupled to each of said inductancesfor normal inductive damping of each of said inductances tosubstantially prevent the translation of signals from said R.-F.circuits and responsive to signals from said control source to preventsaid inductive damping of each of said inductances in sequence, andmixing means coupled to each inductance for providing to a common loadthe signals supplied in sequence from said inductances.

References Cited in the file of this patent UNITED STATES PATENTS1,959,281 Willoughby May 15, 1934 2,157,312 Wright May 9, 1939 2,246,905Uehling June 24, 1941 2,432,560 Crooks Dec. 16, 1947 2,439,561 ChesseyApr. 13, 1948 2,439,651 Dome Apr. 13, 1948 2,627,061 Radigan Jan. 27,1953

